This article is about the different body types of ponies. G1 especially has a large variety of body types. Some are so different in fact that a certain genuine My Little Ponies can be easily passed up at the flea market, the Hasbro copyright doesn't help if you don't think to check for it!
This page is pretty much an English language version of the pony body type page by Myrskytär, http://www.elisanet.fi/myrskytar/